Hey all

Just starting to sort out the tune properly on my 850.
I fitted a new Powerspark distributor (25D) with electronic module, and changed it to a negative earth system while I was at it.

New plugs, new leads, new coil.
Everything sweet.

What is not sweet, however, are the spar plugs.
Cyl 1 and 2 are very rich. A very sooty plug.
Cyl 3 and 4 are pretty spot on - absolutely clean.

It has 19° advance at 1000 rpm - as per a workshop manual which seemed to me extremely advanced for an 850.
.... What do we think?

Any help appreciated.

1 and 2 down on compression compared to 3 and 4?

Have you got twin carbs?

I'm yet to do a compression test.

And only a single HS2 on this wheezy girl.
I sprayed WD40 around the inlet manifold to head area and there was no difference in noise, so I don't think there is a manifold sealing issue but I can't be certain until I pull it off and change it.

Rather than wd40, use carb cleaner.
I would also check your gaps on the plugs along with swapping them over in the cylinders. I found a few plugs recently aren't quite doing what they are supposed to.

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35 thou on each plug, which is about right for an elec dizzy I would have thought.

I'll try testing new plugs to see if there is a plug fault.

If you get any misfiring during warmup, reduce plug gap to .030".

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Cheers Doc I'll keep that in mind.

Do you think 19 degrees (at 1000rpm) on a strobe is far too advanced?

Probably is, for a stock motor.
My 1360 (has bathtubbed race head) was running 20deg static when I had the Pulsar dizzy in. Since fitting the Accuspark black box I've dropped that back a bit, but it still has 20deg @1000rpm.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Also be sure to check your rocker clearance.
But I'd do a compression test as a first port of call.

Check your plug lead resistance. Old cheapo carbonized string ones increase resistance with age, eventually this reduces spark energy and plugs foul easily.
I like Bosch (or similar) inductive core leads. They don't do this.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

what state was it in before you started working on it?

were the old plugs in the same condition (2 good, 2 bad) when you took them out?

have you checked the compression on all 4 yet?

have you swapped the plugs and leads around yet?

I've noticed that 850's are set up with a lot of advance as per the book - I assumed it was because they don't breathe very well with their little valves and a tiny bore, and then with the low compression don't get a very fast burn, so running a lot of advance gives it plenty of time to ignite and burn all of the fuel before the piston gets to the top... or something

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did I tell you that I won a trophy?